Many callers of resolve_revset() and evaluate_revset() will be migrated to
this wrapper. "single" and "default_single" APIs won't be replaced because
they require more contexts to construct error messages.

id_prefix_context() now uses bare revset::parse() to avoid dependency cycle.

…sion

This pattern is common, and most callers of evaluate_revset() can now be
migrated to the wrapper API.

evaluate_programmatic() should be allowed here. AFAIK, the contract is that
the expression should never contain any bare symbols and "fallible" symbol-like
expressions, which doesn't apply to branches() and remote_branches() functions.

evaluate_revset() is removed because there are no callers. However, it's simple
and basic function, so we might want to reintroduce it if needed.